Conductive lubricant composition

ABSTRACT

The present invention provides a conductive lubricant composition, characterized in that the composition contains a lubricating base oil (A) other than a silicone oil, and a non-metallic antistatic agent (B), and exhibits a kinematic viscosity of 25 mm 2 /s or less at 40° C., a viscosity index of 100 or higher, a flash point of 150° C. or higher, and a volume resistivity of 1×10 10  Ω·cm or less at 25° C. The invention also provides a bearing oil formed from the lubricant composition.

TECHNICAL FIELD

The present invention relates to a conductive lubricant composition and,more particularly, to a conductive lubricant composition suitable for abearing oil such as a fluid bearing oil or an oil-impregnated sinteredbearing oil.

BACKGROUND ART

In recent years, roller bearings such as fluid bearings andoil-impregnated sintered bearings have often been employed as bearingsof spindle motors for a magnetic disk, an optical disk, etc., since suchroller bearings realize silent operation and durability.

In the above bearings, a shaft is not in direct contact with the bearinginner surface but is in contact therewith by the mediation of lubricant,which sustains a load applied to the shaft, thereby reducing frictionbetween the shaft and the bearing.

Thus, the performance of the bearings greatly depends on the performanceof lubricating oil.

Requirements in performance of the lubricating oil for use in the rollerbearings include viscosity, durability, and antistatic property.

Among these requirements, viscosity is an essential factor fordetermining electric power loss and bearing toughness of a spindlemotor. In a recent year-by-year trend toward increasing rotation speed(to a range of 10,000 to 50,000 rpm) of spindle motors for use ininformation-related apparatuses (particularly CD apparatuses, DVDapparatuses, HDDs, and laser printers (polygon mirror), a lubricatingoil of low viscosity is selected so as to reduce electric power lossduring high-speed operation.

In general, when the viscosity of lubricating oil decreases, the amountof vaporized oil increases.

Thus, when a low-viscosity lubricating oil is employed, loss of thelubricating oil increases, resulting in a lubrication failure, and inthe worst case, damage to bearings.

Under such circumstances, there have been proposed a large number oflubricating base oils for bearings satisfying both low viscosity and lowvolatility; for example, ester compounds (Japanese Patent ApplicationLaid-Open (kokai) No. 11-315292, p. 1), monoesters (ditto No.2000-63860, p. 1), carbonate esters (ditto No. 2001-107046, p. 1), useof poly(α-olefin) and an ester in combination (ditto Nos. 2001-172656,p. 1 and 2001-240885, p. 1), use of a diester and a polyol ester incombination (ditto No. 2001-279284, p. 1), neopentyl glycol esters(ditto No. 2001-316687, p. 1), an aromatic ester or diester (ditto No.2002-97482, p. 1), monoesters (ditto No. 2002-146381, paragraph [0007]),and specific diesters formed from oxalic acid, malonic acid, succinicacid, etc. (ditto No. 2002-155944, p. 1).

Meanwhile, in a roller bearing, a shaft and a bearing are completelyseparated by lubricating oil film.

Therefore, static electricity tends to be generated by movement offluid. When the thus-generated electricity is discharged, essentialelectronic parts and magnetic parts (e.g., MR head of a hard disk drive)may become disordered.

Thus, static charge of roller bearings for use in precision machinessuch as a magnetic disk apparatus must be caused to flow to ground, tothereby protect electronic and magnetic apparatuses against staticelectricity.

From this viewpoint, the aforementioned conventional bearing lubricatingoils still have the problem that they have problematically large volumeresistivity, which readily induces generation of static electricity,although they satisfy both low viscosity and low volatility.

In order to solve the above problem, a lubricating oil to whichconductive microparticles of a metal or a metal oxide have been added isreported (see, for example, Japanese Patent Application Laid-Open(kokai) No. 10-30096, p. 1 or 11-315292, paragraph [0023]). However,when a lubricating oil containing such microparticles is employed,microparticles present on the sliding surface cause anomalous wear ofthe bearing during start and stop of the motor.

A lubricating oil containing a metal organic salt such as sulfonate,phenate, or salicylate, instead of such metallic particles, has alsobeen proposed (see Japanese Patent Application Laid-Open (kokai)2001-234187, p. 1).

However, the above metal organic salt antistatic agent can exhibitantistaticity only when added in a large amount.

In addition, during long-term use of the lubricating oil, the antistaticagent problematically forms an inorganic salt (sludge), which isinsoluble in oil.

The present invention has been accomplished in an attempt for solvingthe aforementioned problems, and an object of the present invention isto provide a conductive lubricant composition which, without impairingroller bearing oil performance, prevents anomalous wearing, generationof sludge, and occurrence of static electricity which would otherwise begenerated by movement of fluid.

DISCLOSURE OF THE INVENTION

The present inventors have carried out extensive studies in order toattain the aforementioned object, and have found that the above objectcan be attained by adding a non-metallic antistatic agent to alubricating oil, and limiting specific characteristics to fall withinspecific ranges. The present invention has been accomplished on thebasis of this finding.

Accordingly, the present invention provides a conductive lubricantcomposition, characterized in that the composition comprises alubricating base oil (A) other than a silicone oil, and a non-metallicantistatic agent (B), and exhibits a kinematic viscosity of 25 mm²/S orless at 40° C., a viscosity index of 100 or higher, a flash point of150° C. or higher, preferably 200° C. or higher, and a volumeresistivity of 1×10¹⁰ Ω·cm or less at 25° C.

The present invention also provides a bearing oil comprising thelubricant composition.

BEST MODES FOR CARRYING OUT THE INVENTION

The conductive lubricant composition of the present invention comprisesa lubricating base oil (A) and a non-metallic antistatic agent (B). Thecomposition must satisfy at least the following characteristicrequirements (1) to (4).

(1) The lubricant composition of the present invention essentiallyexhibits a kinematic viscosity of 25 mm²/s or less at 40° C., preferably22 mm²/s or less, particularly preferably 10 mm²/s or less.

When the kinematic viscosity is higher than 25 mm²/S, the lubricatingbase oil has an excessively high viscosity, thereby failing to attainsufficient electricity-saving effect.

(2) The lubricant composition of the present invention essentiallyexhibits a viscosity index of 100 or higher, preferably 120 or higher,more preferably 125 or higher, particularly 130 or higher.

When the viscosity index is lower than 100, change in viscosity withrespect to temperature change increases.

(3) The lubricant composition of the present invention essentiallyexhibits a flash point (as determined through COC method) of 150° C. orhigher.

When the flash point is lower than 150° C., a large amount oflubricating base oil is vaporized during use, thereby shortening thelife time of the lubricant composition.

(4) The lubricant composition of the present invention essentiallyexhibits a volume resistivity of 1×10¹⁰ Ω·cm or less at 25° C.

When the volume resistivity is in excess of 1×10¹⁰ Ω·cm, antistaticperformance decreases.

Moreover, the lubricating base oil of the present invention preferablyexhibits a pour point, as measured in accordance with JIS K2265, of −30°C. or lower, more preferably −40° C. or lower.

The lubricating base oil, serving as component (A) employed in thelubricant composition of the present invention satisfying the aboverequirements, preferably contains a compound formed of carbon, hydrogen,and oxygen (hereinafter the compound is referred to as “anoxygen-containing compound”).

Specifically, the oxygen-containing compound is preferably an etherether, an ester, or a compound having a carbonate moiety, with an ethercompound being particularly preferred.

Specific examples of the ester compound which is preferably employedinclude polyol esters produced through condensation between a polyhydricalcohol such as neopentyl glycol, trimethylolpropane, or pentaerythritoland a fatty acid; diesters produced through condensation between adibasinc acid such as adipic acid or sebacic acid and a monohydrocalcohol; and monoesters produced through a fatty acid and a monohydricalcohol.

The ether compound is preferably any of the compounds represented by thefollowing formula (I), or a mixture thereof.R¹—O—(R²—O)_(a)—(R³—O)_(b)—(R⁴—O)_(c)—R⁵  (I)

In formula (I), each of R¹ and R⁵ represents hydrogen, a C1-C24 alkylgroup, a phenyl group, or a C7-C24 alkylaryl group; each of R², R³, andR⁴ represents a C2-C18 alkylene group; each of a, b, and c is 0 to 8(preferably 0 to 5); and the sum of a to c is 0 to 8 (preferably 0 to5).

The units (R²—O), (R³—O), and (R⁴—O) may be identical to or differentfrom one another.

The alkyl group represented by R¹ or R⁵ may be linear, branched, orcyclic. Examples of the alkyl group include methyl, ethyl, propyl,butyl, hexyl, 2-ethylhexyl, 3,5,5-trimethylhexyl, heptyl, octyl,3,7-dimethyloctyl, nonyl, 2-pentylnonyl, decyl, 2-octylundecanyl,dodecyl, cyclopentyl, and cyclohexyl. Among them, 2-ethylhexyl,3,5,5-trimethylhexyl, octyl, 3,7-dimethyloctyl, nonyl, 2-pentylnonyl,decyl, and 2-octylundecanyl are particularly preferred.

Examples of the alkylaryl group represented by R¹ or R⁵ includealkylphenyl and alkylnaphthyl. Exampled of the alkyl moiety of thealkylaryl group include the groups described above. Among them, octyl,decyl, and dodecyl are particularly preferred.

The alkylene group represented by R², R³, or R⁴ may be linear, branched,or cyclic. Examples of the alkylene group include ethylene, propylene,butylene, hexylene, nonylene, decylene, dodecylene, cyclopentylene, andcyclohexylene. Of these, ethylene, propylene, butylene, hexylene,nonylene, and decylene are particularly preferred.

The ether compound is preferably a monoether compound represented byformula (II).R⁶—O—R⁷  (II)

In formula (II), one of R⁶ and R⁷ is a C1 to C24 alkyl group, and theother is a C1 to C24 alkyl group, a phenyl group, or a C7 to C24alkylaryl group.

The ether compounds represented by formulas (I) and (II) may be usedsingly or in combination.

These ether compounds may be used in combination with the estercompound.

The ether compound and/or the ester compound may be incorporated in atotal amount of 20 to 80 mass % based on the hydrocarbon base material.

The lubricating base oil of the present invention may contain, inaddition to the oxygen-containing compound, any of a variety ofhydrocarbon compounds.

In this case, the lubricating base oil must satisfy the above-mentionedrequirements (1) to (4).

No particular limitation is imposed on the hydrocarbon compound to bemixed with the oxygen-containing compound, so long as the hydrocarboncompound does not impair the effects of the lubricating base oil of thepresent invention. Examples of the hydrocarbon compound include mineraloils (e.g., 80 neutral mineral oils), poly(α-olefin) (e.g., viscositygrade 4 mm²/s or 8 mm²/s (100° C.)), ethylene-propylene copolymers, andalkylbenzenes (e.g., propylbenzene and butylbenzene). Of these,poly(α-olefin) is preferred.

The lubricating base oil of the present invention excludes silicone oil.

The reason for exclusion is that, even though silicone oil satisfies theaforementioned requirements, silicone oil exhibits poor lubricity.

In the present invention, the non-metallic antistatic agent (B) to beadded to the lubricating base oil (A) is preferably an amine derivative,a succinic acid derivative, a poly(oxyalkylene) glycol, or a polyhydricalcohol partial ester. The antistatic agent is preferably incorporatedin an amount of 0.01 to 10 mass % on the basis of entire amount of thecomposition.

Specific examples of the amine derivative includepoly(oxyethylene)alkylamines represented by the following formula:

(wherein R⁸ represents a C1 to C18 alkyl group),poly(oxyethylene)alkylamides represented by the following formula:

(wherein R⁹ represents a C1 to C18 alkyl group), and condensatesproduced from a polyethyleneimine such as tetraethylenepentamine (TEPE)and a fatty acid. Of these, a condensate produced from TEPE and stearicacid is preferred.

Examples of preferred succinic acid derivatives includepolybutenylsuccinimide.

The poly(oxyalkylene) glycol is preferably a compound represented byformula (III), or a mixture thereof.R¹—O—(R²—O)_(d)—(R³—O)_(e)—(R⁴—O)_(f)—R⁵  (III)

In formula (III), R¹ to R⁵ have the same meanings as defined in relationto formula (I); each of d, e, and f is 0 to 50; and the sum of d to f is9 to 50.

The units (R²—O), (R³—O), and (R⁴—O) may be identical to or differentfrom one another.

Among these compounds, poly(oxyethylene) alkyl ether R¹⁰ (CH₂CH₂O)_(n)H(wherein R¹⁰ represents a C1 to C18 alkyl group, and n is a number of 1to 10); poly(oxyethylene) alkyl phenyl ether R¹¹-Q-O(CH₂CH₂O)_(n)H(wherein R¹¹ is a C1 to C18 alkyl group, Q represents an aromaticresidue, and n is a number of 1 to 10); and poly(oxyethylene) glycolfatty acid ester R¹²COO(CH₂CH₂O)_(n)H (wherein R¹² is a C1 to C18 alkylgroup, and n is a number of 1 to 10) are more preferred.

Examples of the polyhydric alcohol partial ester include sorbitan fattyacid esters such as sorbitan monoleate and sorbitan dioleate representedby the following formula:

(wherein R¹³ is a C1 to C18 alkyl group, and each of n and m is a numberof 1 to 10); glycerin fatty acid esters such as glycerin monoleate andglycerin dioleate represented by the following formula:

(wherein R¹⁴ is a C1 to C18 alkyl group, and each of n and m is a numberof 1 to 10); and partial ester compounds produced from a polyhydricester such as pentyl glycol, trimethylolpropane, or pentaerythritol anda C1 to C24 fatty acid.

Among lubricant compositions falling within the scope of the presentinvention, a composition including a monoether having alkyl groups(component A) and a condensate produced from tetraethylenepentamine anda fatty acid (e.g., stearic acid (component (B)) is particularlypreferred, from the viewpoint of low viscosity, low volatility, heatresistance, and antistaticity.

Preferably, an additive other than the aforementioned additive is added,in accordance with needs, to the lubricating base oil of the presentinvention, to thereby form a lubricant composition, which is employed asuses of interest.

Any of known additives may be used, and examples include antioxidants,oiliness agents, friction reducers, rust preventives, metaldeactivators, defoaming agents, and viscosity index improvers, asdescribed below.

(1) Examples of the antioxidants include amine-based antioxidants,phenol-based antioxidants, and sulfur compounds.

Examples of the amine-based anti-oxidants includemonoalkyldiphenylamines such as monoctyldiphenylamine andmonononyldiphenylamine; dialkyldiphenylamines such as4,4′-dibutyldiphenylamine, 4,4′-dipentyldiphenylamine,4,4′-dihexyldiphenylamine, 4,4′-diheptyldiphenylamine,4,4′-dioctyldiphenylamine, and 4,4′-dinonyldiphenylamine;polyalkyldiphenylamines such as tetrabutyldiphenylamine,tetrahexyldiphenylamine, tetraoctyldiphenylamine, andtetranonyldiphenylamine; and naphtylamines such as α-naphthylamine,phenyl-α-naphtylamine, butylphenyl-α-naphtylamine,pentylphenyl-α-naphtylamine, hexylphenyl-α-naphtylamine,heptylphenyl-α-naphtylamine, octylphenyl-α-naphtylamine, andnonylphenyl-α-naphtylamine. Of these, dialkyldiphenylamines arepreferred.

The above amine-based anti-oxidants may be used singly or in combinationof two or more species.

Examples of the phenol-based anti-oxidants include monophenolicanti-oxidants such as 2,6-di-tert-butyl-4-methylphenol,2,6-di-tert-butyl-4-ethylphenol, and 2,6-di-tert-butyl-p-cresol; anddiphenolic anti-oxidants such as4,4′-methylenebis(2,6-di-tert-butylphenol) and2,2′-methylenebis(4-ethyl-6-tert-butylphenol).

The above phenol-based anti-oxidants may be used singly or incombination of two or more species.

Examples of the sulfur compounds include phenothiazine,pentaerythritol-tetrakis(3-laurylthiopropionate),bis(3,5-tert-butyl-4-hydroxybenzyl) sulfide,thiodiethylenebis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)) propionate, and2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazine-2-methylamino)phenol.

The antioxidant(s) are preferably incorporated in an amount of 0.01 to10 mass % based on the total amount of the composition, particularlypreferably 0.03 to 5 mass %.

(2) Examples of the oiliness agents aliphatic saturated and unsaturatedmonocarboxylic acids such as stearic acid and oleic acid; polymerizedfatty acids such as dimer acid and hydrogenated dimer acid; hydroxyfattyacids such as ricinoleic acid and 12-hydroxystearic acid; aliphaticsaturated and unsaturated monoalcohols such as lauryl alcohol and oleylalcohol; aliphatic saturated and unsaturated monoamines such asstearylamine and oleylamine; and aliphatic saturated and unsaturatedmonocarbamides such as laurylamide and oleylamide.

The oiliness agent(s) are preferably incorporated in an amount of 0.01to 10 mass % based on the total amount of the composition, particularlypreferably 0.1 to 5 mass %.

(3) Examples of the friction modifiers which may be employed includeagents generally employed as oiliness agents or extreme pressure agents,more particularly, phosphate esters, amine salts of phosphate ester, andsulfur-containing extreme pressure agents.

The phosphate esters include phosphate esters, acid phosphate esters,phosphite esters, and acid phosphite esters represented by the followingformulas (IV) to (VIII):

(wherein R¹⁵ to R¹⁷, which may be identical to or different from oneanother, each represents a C4 to C30 alkyl group, an alkenyl group, analkylaryl group, or an arylalkyl group).

Examples of the phosphate esters include triaryl phosphates, trialkylphosphates, trialkylaryl phosphates, triarylalkyl phosphates, andtrialkenyl phosphates. Specific examples include triphenyl phosphate,tricresyl phosphate, benzyl diphenyl phosphate, ethyl diphenylphosphate, tributyl phosphate, ethyl dibutyl phosphate, cresyl diphenylphosphate, dicresyl phenyl phosphate, ethylphenyl diphenyl phosphate,diethylphenyl phenyl phosphate, propylphenyl diphenyl phosphate,dipropylphenyl phenyl phosphate, triethylphenyl phosphate,tripropylphenyl phosphate, butylphenyl diphenyl phosphate, dibutylphenylphenyl phosphate, tributylphenyl phosphate, trihexyl phosphate,tri(2-ethylhexyl) phosphate, tridecyl phosphate, trilauryl phosphate,trimyristyl phosphate, tripalmityl phosphate, tristearyl phosphate, andtrioleyl phosphate.

Examples of the acid phosphate esters include 2-ethylhexyl acidphosphate, ethyl acid phosphate, butyl acid phosphate, oleyl acidphosphate, tetracosyl acid phosphate, isodecyl acid phosphate, laurylacid phosphate, tridecyl acid phosphate, stearly acid phosphate, andisostearyl acid phosphate.

Examples of the phosphite esters include triethyl phosphite, tributylphosphite, triphenyl phosphite, tricresyl phosphite, tri(nonylphenyl)phosphite, tri(2-ethylhexyl) phosphite, tridecyl phosphite, trilaurylphosphite, triisooctyl phosphite, diphenyl isodecyl phosphite,tristearyl phosphite, and trioleyl phosphite.

Examples of the acid phosphite esters include dibutyl hydrogenphosphite, dilauryl hydrogen phosphite, dioleyl hydrogen phosphite,distearyl hydrogen phosphite, and diphenyl hydrogen phosphite.

Among these phosphate esters, tricresyl phosphate and triphenylphosphate are preferred.

Examples of the amines which form amine salts with the phosphate estersinclude monosubstituted amines, disubstituted amines, and trisubstitutedamines, which are represented by formula (IX):R⁸ _(p)NH_(3-p)  (IX)(wherein R¹⁸ represents a C3 to C30 alkyl group or alkenyl group, a C6to C30 aryl group or arylalkyl group, or a C2 to C30 hydroxyalkyl group;p is 1, 2, or 3; when a plurality of R¹⁸s are present, these R¹⁸s may beidentical to or different from one another).

The C3 to C30 alkyl or alkenyl group represented by R¹⁸ in formula (IX)may be linear, branched, or cyclic.

Examples of the monosubstituted amines include butylamine, pentylamine,hexylamine, cyclohexylamine, octylamine, laurylamine, stearylamine,oleylamine, and benzylamine. Examples of the disubstituted aminesinclude dibutylamine, dipentylamine, dihexylamine, dicyclohexylamine,dioctylamine, dilaurylamine, distearylamine, dioleylamine,dibenzylamine, stearylmonoethanolamine, decylmonoethanolamine,hexylmonopropanolamine, benzylmonoethanolamine, phenylmonoethanolamine,and tolylmonopropanol. Examples of the trisubstituted amines includetributylamine, tripentyl amine, trihexylamine, tricyclohexylamine,trioctylamine, trilaurylamine, tristearylamine, trioleylamine,tribenzylamine, dioleylmonoethanolamine, dilaurylmonopropanolamine,dioctylmonoethanolamine, dihexylmonopropanolamine,dibutylmonopropaolamine, oleyldiethanolamine, stearyldipropanolamine,lauryldiethanolamine, octyldipropanolamine, butyldiethanolamine,benzyldiethanolamine, phenyldiethanolamine, tolyldipronanolamine,xylyldiethanolamine, triethanolamine, and tripropanolamine.

The sulfur-containing extreme pressure may be any compound having asulfur atom in the molecule thereof, so long as the compound can bedissolved or uniformly dispersed in a lubricating base oil and canexhibit extreme pressure performance and excellent frictioncharacteristics.

Examples of the sulfur-containing compound include sulfidized fats andoils, sulfidized fatty acid, sulfidized esters, sulfidized olefins,dihydrocarbyl polysulfides, thiadiazole compounds, thiophosphate esters(thiophosphites and thiophosphates), alkyl thiocarbamoyl compounds,thiocarbamate compounds, thioterpene compounds, and dialkylthiodipropionate compounds.

The sulfidized fats and oils are produced through reaction of a fat oran oil (e.g., lard, whale oil, vegetable oil, or fish oil) with sulfuror a sulfur-containing compound. Although no particular limitation isimposed on the sulfur content, the content preferably 5 to 30 mass %.

Specific examples include sulfidized lard, sulfidized rape seed oil,sulfidized castor oil, sulfidized soy bean oil, and sulfidized rice branoil.

Examples of the sulfidized fatty acids include sulfidized oleic acid.Examples of the sulfidized esters include sulfidized methyl oleate andsulfidized octyl ester of rice bran fatty acid.

Examples of the sulfidized olefins include compounds represented by thefollowing formula (X):R¹⁹—S_(q)—R²⁰  (X)(wherein R¹⁹ represents a C2 to C15 alkenyl group, R²⁰ represents a C2to C15 alkyl group or alkenyl group; and q is an integer of 1 to 8).

These compounds are produced reaction between a C2 to C15 olefin or adimer to tetramer thereof and a sulfidizing agent such as sulfur orsulfur chloride. Preferred olefins are propylene, isobutene, anddiisobutene.

Examples of the dihydrocarbyl polysulfides include compounds representedby the following formula (XI):R²¹—S_(r)—R²²  (XI)(wherein R²¹ and R²², which may be identical to or different from eachother, each represents a C1 to C20 alkyl group or cyclic alkyl group, aC6 to C20 aryl group, a C7 to C20 alkyl aryl group, or a C7 to C20arylalkyl group; and r is an integer of 1 to 8).

When each of R²¹ and R²² an alkyl group, the compound is called alkylsulfide.

Examples of the group represented by R²¹ or R²² in formula (XI) includemethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl,tert-butyl, pentyl groups, hexyl groups, heptyl groups, octyl groups,nonyl groups, decyl groups, dodecyl groups, cyclohexyl, cyclooctyl,phenyl, naphthyl, tolyl, xylyl, benzyl, and phenetyl.

Examples of preferred dihydrocarbyl polysulfides include dibenzylpolysulfides, dinonyl polysulfides, dodecyl polysulfides, dibutylpolysulfides, dioctyl polysulfides, diphenyl polysulfides, anddicyclohexyl polysulfided.

Examples of preferred thiadiazole compounds include 1,3,4-thiadiazole,1,2,4-thiadiazole compound, and 1,4,5-thiadiazole represented by thefollowing formula (XII):

(wherein each of R²³ and R²⁴ represents a hydrogen atom, a C1 to C20hydrocarbon group; and each of f and g is an integer of 0 to 8).

Specific examples of preferred thiadiazole compounds include2,5-bis(n-hexyldithio)-1,3,4-thiadiazole,2,5-bis(n-octyldithio)-1,3,4-thiadiazole,2,5-bis(n-nonyldithio)-1,3,4-thiadiazole,2,5-bis(1,1,3,3-tetramethylbutyldithio)-1,3,4-thiadiazole,3,5-bis(n-hexyldithio)-1,2,4-thiadiazole,3,5-bis(n-octyldithio)-1,2,4-thiadiazole,3,5-bis(n-nonyldithio)-1,2,4-thiadiazole,3,5-bis(1,1,3,3-tetramethylbutyldithio)-1,2,4-thiadiazole,4,5-bis(n-hexyldithio)-1,2,3-thiadiazole,4,5-bis(n-octyldithio)-1,2,3-thiadiazole,4,5-bis(n-nonyldithio)-1,2,3-thiadiazole, and4,5-bis(1,1,3,3-tetramethylbutyldithio)-1,2,3-thiadiazole.

Examples of the thiophosphate esters include alkyl trithiophosphites,aryl or alkyl arylthiophosphates, dilauryl dithiophosphate zinc salts,with lauryl trithiophosphites and triphenyl thiophosphate beingparticularly preferred.

Examples of the alkyl thiocarbamoyl compounds include compoundsrepresented by the following formula (XIII):

(wherein each of R²⁵ to R²⁸ represents a C1 to C20 alkyl group, and h isan integer of 1 to 8).

Examples of preferred alkyl thiocarbamoyl compounds includebis(dimethylthiocarbamoyl) monosulfide, bis(dibutylthiocarbamoyl)monosulfide, bis(dimethylthiocarbamoyl) disulfidebis(dibutylthiocarbamoyl) disulfide, bis(diamylthiocarbamoyl) disulfide,and bis(octylthiocarbamoyl) disulfide.

Examples of the thiocarbamate compound compounds include zinc dialkylthithiacarbamate. Examples of the thioterpene compounds include areaction product of phosphorus pentasulfide and pinene. Examples of thedialkyl thiodipropionate compounds include dilauryl thiodipropionate anddistearyl thiodipropionate.

Among them, thiadiazole compounds and benzyl sulfide are preferred, fromthe viewpoint of extreme pressure performance, friction characteristics,and stability against thermal oxidation, etc.

The friction modifier(s) are preferably incorporated in an amount of0.01 to 10 mass % based on the total amount of the composition,particularly preferably 0.05 to 5 mass %.

When the amount is less than 0.01 mass %, improvement of frictioncharacteristics by virtue of a synergistic effect with other componentsmay be insufficient, whereas when the amount is in excess of 10 mass %,improvement of the effect commensurate with addition may fail to beattained.

(4) Examples of rust preventives which may be employed include alkyl andalkenyl succinate derivatives such as dodecenyl succinate half esters,otcadecenyl succinic anhydride, and dodecenylsuccinamide; polyhydricalcohol partial esters such as sorbitan monooleate, glycerin monoolate,and pentaerythritol monooleate; amines such as rosin amines andN-oleylsarcosine; and dialkyl phosphite amine salts.

The rust preventive(s) are preferably incorporated in an amount of 0.01to 5 mass % based on the total amount of the composition, particularlypreferably 0.05 to 2 mass %.

(5) Examples of the metal deactivator which may be employed in theinvention include benzotriazoles, thiadiazoles, and gallic acid esters.

The metal deactivator(s) are preferably incorporated in an amount of0.01 to 0.4 mass % based on the total amount of the composition,particularly preferably 0.01 to 0.2 mass %.

(6) Examples of the defoaming agent which may be employed in theinvention include liquid silicone, and thus methylsilicone,fluorosilicone, and polyacrylate may be employed.

The defoaming agent(s) are preferably incorporated in an amount of0.0005 to 0.01 mass % based on the total amount of the composition.

(7) Examples of the viscosity index improver which may be employed inthe present invention include olefin copolymers such as poly(alkylmethacrylate), polyalkylstyrene, polybutene, ethylene-propylenecopolymer, styrene-diene copolymer, and styrene-maleic anhydride estercopolymer.

The viscosity index improver(s) are preferably incorporated in an amountof 0.1 to 15 mass % based on the total amount of the composition,particularly preferably 0.5 to 7 mass %.

The conductive lubricant composition of the present invention issuitably employed as a bearing oil such as a fluid bearing oil or anoil-impregnated sintered bearing oil.

The present invention will next be described in more detail by way ofexamples, which should not be construed as limiting the inventionthereto.

1. Characteristics of lubricating oils were determined through thefollowing methods.

(1) Kinematic viscosity

Determined at 40° C. in accordance with JIS K2283

(2) Viscosity index

Determined in accordance with JIS K2283

(3) Flash point (COC method)

Determined in accordance with JIS K2265

(4) Pour point

Determined in accordance with JIS K2269

(5) Volume resistivity

Determined in accordance with JIS C2102

(6) Thin film residue test (percent oil retention, heat resistanceevaluation)

A contained and a thermostat air bath, which are stipulated in thelubricating oil stability test (JIS K2504), were employed. A sample (1g) was left to stand at 80° C. for 1,000 hours, followed by measuringthe amount of remaining oil.

Percent oil retention was obtained from the amount.

Appearance of the oil sample after a 1,000-hour test was observed, andformation of sludge insoluble in the oil was checked.

During the test, air was continuously fed at 10 L/hr to the thermostatair bath.

2. Structural analysis

The compounds produced in the following Production Examples wereidentified to have a purity of 99% or higher on the basis of a peak areaobtained by use of a gas chromatograph (Hitachi: model 263-70, column:OV-1 packed column (2 m), product of GL Science Inc.). The structure ofeach compound was determined by use of a nuclear magnetic resonanceapparatus (¹H-NMR, ¹³C-NMR: GSX400, product of JEOL Ltd.).

3. Production Examples

PRODUCTION EXAMPLE 1

2-Octyl-1-dodecanol (300 g), 1-bromooctane (300 g), tetrabutylammoniumbromide (30 g), and an aqueous sodium hydroxide solution (500 g) (sodiumhydroxide (150 g) dissolved in water (350 g)) were placed in a 2-L glassflask, and the mixture was allowed to react under stirring for 20 hoursat 50° C.

After completion of reaction, the reaction mixture was transferred to aseparating funnel, and the aqueous layer was separated throughfiltration. The remaining organic layer was washed five times with water(500 mL).

The organic layer was distilled under reduced pressure, to therebyseparate an ether compound having the following structure.

PRODUCTION EXAMPLE 2

2-Hexyl-1-decanol (300 g), 1-bromodecane (300 g), tetrabutylammoniumbromide (30 g), and a 30% aqueous sodium hydroxide solution (500 g)(sodium hydroxide (150 g) dissolved in water (350 g)) were placed in a2-L glass flask, and the mixture was allowed to react under stirring for20 hours at 50° C.

After completion of reaction, the reaction mixture was transferred to aseparating funnel, and the aqueous layer was separated throughfiltration. The remaining organic layer was washed five times with water(500 mL).

The organic layer was distilled under reduced pressure, to therebyseparate an ether compound having the following structure.

PRODUCTION EXAMPLE 3

2-Octyl-1-dodecanol (300 g), 1-bromodecane (300 g), tetrabutylammoniumbromide (30 g), and a 30% aqueous sodium hydroxide solution (500 g)(sodium hydroxide (150 g) dissolved in water (350 g)) were placed in a2-L glass flask, and the mixture was allowed to react under stirring for20 hours at 50° C.

After completion of reaction, the reaction mixture was transferred to aseparating funnel, and the aqueous layer was separated throughfiltration. The remaining organic layer was washed five times with water(500 mL).

The organic layer was distilled under reduced pressure, to therebyseparate an ether compound having the following structure.

4. Base oils and additives

Base oils and additives employed in the following Examples andComparative Examples are listed in Tables 1 and 2. TABLE 1 Base oilCompounds Base oil A-1 Compound synthesized in Production Example 1 Baseoil A-2 Compound synthesized in Production Example 2 Base oil A-3Compound synthesized in Production Example 3 Base oil B Neopentyl glycoldipelargonate Base oil C Dioctyl sebacate Base oil D 1-Dodecene dimer,polyα-olefin Base oil E High-pure mineral oil obtained throughhydroreformation of paraffin crude oil

TABLE 2 Additive Compounds Antioxidant Phenyl α-naphtylamine Rustpreventive Sorbitan monooleate Friction modifier A di(mono)methyl acidphosphate amine salt [mono:di = 50:50(mol)] Friction modifier BDi-t-nonyl polysulfide Antistatic agent A Neutral barium sulfonate (basevalue 1) Antistatic agent B polybutenylsuccinimide Antistatic agent CTetraethylenepentamine-stearic acid condensate

EXAMPLES 1 TO 12 AND COMPARATIVE EXAMPLES 1 TO 6

Lubricant compositions were prepared in accordance with the formulationslisted in Tables 3, and the aforementioned characteristics (1) to (6)were determined.

The results are shown in Tables 3. TABLE 3-1 Lubricant composition(parts by mass) Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Base oil A-1 99.8Base oil A-2 98.8 98.8 Base oil A-3 98.8 Base oil B 98.8 Base oil C 98.8Base oil D Base oil E Anti-oxidant 1 1 1 1 Rust preventive Frictionmodifier A Friction modifier B Antistatic agent A Antistatic agent B 0.2Antistatic agent C 0.2 0.2 0.2 0.2 0.2 (Total) 100 100 100 100 100 100Kinematic viscosity (mm²/s) 9.79 8.387 8.41 11.73 8.75 11.6 at 40° C.Viscosity index 138 129 129 146 136 153 Flash point 212 209 207 218 220220 (COC method) (° C.) Pour point (° C.) −30 −45 −45 −27.5 −40 −50>Volume resistivity (×10¹⁰ Ω · cm) 0.21 0.12 0.1 0.38 0.22 0.14 Thin filmresidue test (80° C., 500 hr) Percent oil retention (mass %) 94.54 88.5395.34 98.47 94.63 99.5 Appearance (sludge) No No No No No No

TABLE 3-2 Lubricant composition (parts by mass) Ex. 7 Ex. 8 Ex. 9 Ex. 10Ex. 11 Ex. 12 Base oil A-1 Base oil A-2 68.8 68.8 97.75 67.7 67.75 Baseoil A-3 Base oil B 30 98.75 30 Base oil C Base oil D 30 30 Base oil EAnti-oxidant 1 1 1 1 1 1 Rust preventive 1 1 1 Friction modifier A 0.050.05 0.05 Friction modifier B 0.05 0.05 Antistatic agent A Antistaticagent B Antistatic agent C 0.2 0.2 0.2 0.2 0.2 0.2 (Total) 100 100 100100 100 100 Kinematic viscosity (mm²/s) 8.58 8.71 8.851 9.009 8.49 8.95at 40° C. Viscosity index 131 112 123 132 131 112 Flash point 214 205204 210 211 204 (COC method) (° C.) Pour point (° C.) −45 −45 −50 −40−45 −45 Volume resistivity (×10¹⁰ Ω · cm) 0.15 0.27 0.0135 0.36 0.01220.014 Thin film residue test (80° C., 500 hr) Percent oil retention(mass %) 95.2 91.44 94.97 94.06 94.83 91.27 Appearance (sludge) No No NoNo No No

TABLE 3-3 Lubricant composition Comp. Comp. Comp. Comp. Comp. Comp.(parts by mass) Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Base oil A-1 Baseoil A-2 Base oil A-3 99 98.8 Base oil B 99 98.8 Base oil C Base oil D98.8 Base oil E 98.8 Anti-oxidant 1 1 1 1 1 1 Rust preventive 1 1Friction modifier A Friction modifier B Antistatic agent A 0.2 0.2Antistatic agent B 0.2 Antistatic agent C 0.2 (Total) 100 100 100 100101 101 Kinematic viscosity (mm²/s) 8.34 11.81 8.41 8.73 9.686 8.135 at40° C. Viscosity index 129 146 129 136 85 80 Flash point 210 218 208 218202 156 (COC method) (° C.) Pour point (° C.) −45 −27.5 −45 −40 −50 −7.5Volume resistivity (×10¹⁰ Ω · cm) 8 12.00 0.73 0.7 0.02 0.0185 Thin filmresidue test (80° C., 500 hr) Percent oil retention (mass %) 99.42 98.299.31 97.86 67.15 20.88 Appearance (sludge) No No Yes Yes No No

INDUSTRIAL APPLICABILITY

As described hereinabove, the conductive lubricant composition of thepresent invention, without impairing roller bearing oil performance, canprevent anomalous wear, generation of sludge, and occurrence of staticelectricity which would otherwise be generated by movement of fluid.Therefore, the conductive lubricant composition is suitable for abearing oil such as a fluid bearing oil or an oil-impregnated sinteredbearing oil.

1. A conductive lubricant composition, characterized in that thecomposition comprises a lubricating base oil (A) other than a siliconeoil, and a non-metallic antistatic agent (B), and exhibits a kinematicviscosity of 25 mm²/s or less at 40° C., a viscosity index of 100 orhigher, a flash point, as determined through the COC method, of 150° C.or higher, and a volume resistivity of 1×10¹⁰ Ω·cm or less at 25° C. 2.A conductive lubricant composition as described in claim 1, whichexhibits a kinematic viscosity of 20 mm²/s or less at 40° C.
 3. Aconductive lubricant composition as described in claim 1, which exhibitsa viscosity index of 120 or higher.
 4. A conductive lubricantcomposition as described in claim 1, which exhibits a pour point of −40°C. or lower.
 5. A conductive lubricant composition as described in claim1, which comprises a lubricating base oil (A) formed of carbon,hydrogen, and oxygen, and 0.01 to 10 mass % of at least one compoundselected from among an amine derivative, a succinic acid derivative, apoly(oxyalkylene) glycol, and a polyhydric alcohol partial ester,serving as a non-metallic antistatic agent (B).
 6. A conductivelubricant composition as described in claim 1, wherein the lubricatingbase oil (A) contains an ester compound.
 7. A conductive lubricantcomposition as described in claim 6, wherein the ester compound is atleast one compound selected from among a polyol ester produced throughcondensation reaction between a polyhydric alcohol and a fatty acid, adiester produced through condensation reaction between a dibasic acidand a monohydric alcohol, and a monoester produced through condensationreaction between a fatty acid and a monohydric alcohol.
 8. A conductivelubricant composition as described in claim 1, wherein the lubricatingbase oil (A) contains an ether compound.
 9. A conductive lubricantcomposition as described in claim 8, wherein the ether compound is acompound represented by formula (I):R¹—O—(R²—O)_(a)—(R³—O)_(b)—(R⁴—O)_(c)—R⁵  (I) (wherein each of R¹ and R⁵represents hydrogen, a C1-C24 alkyl group, a phenyl group, or a C7-C24alkylaryl group; each of R², R³, and R⁴ represents a C2-C18 alkylenegroup; each of a, b, and c is 0 to 8; the sum of a to c is 0 to 8; andthe units (R²—O), (R³—O), and (R⁴—O) may be identical to or differentfrom one another.
 10. A conductive lubricant composition as described inclaim 9, wherein the ether compound is a monoether compound representedby formula (II):R⁶—O—R⁷  (II) (wherein one of R⁶ and R⁷ is a C1 to C24 alkyl group, andthe other is a C1 to C2-4 alkyl group, a phenyl group, or a C7 to C24alkylaryl group).
 11. A conductive lubricant composition as described inclaim 5, wherein the lubricating base oil (A) is an ether compound andthe non-metallic antistatic agent (B) is an amine derivative.
 12. Aconductive lubricant composition as described in claim 5, wherein theamine derivative serving as the non-metallic antistatic agent (B) is acondensate produced from tetraethylenepentamine and a fatty acid.
 13. Aconductive lubricant composition as described in claim 1, wherein thelubricating base oil (A) further contains a hydrocarbon compound.
 14. Aconductive lubricant composition as described in claim 1, which furthercontains at least one additive selected from among an antioxidant, anoiliness agent, a friction reducer, a rust preventive, a metaldeactivator, a defoaming agent, and a viscosity index improver.
 15. Abearing oil comprising a conductive lubricant composition as recited inclaim 1.